Back when he was still in a ~3 gallon vase, Heng Hok developed this habit of sleeping vertically upside down, with his head dug into the marble stones.

Don't worry, there was nothing wrong with him- he just lacked the proper cave decor he so wished for, so he decided to improvise.
Shortly after moving him to a 10 gallon tank, I thought he would break this habit due to the spread out of the marble stones. He proved me wrong:

He decided to sleep vertically upside down in the cup. Such a crazy fish, but what can I do, right?
Of course, this craziness stopped when I got him a little pagoda-cave decor. Now he sleeps in there, where my camera can't find him.